The proposed work involves low temperature magnetic resonance (nur) and electron-nuclei double resonance (endor) investigations of a series of biologically important transition metal complexes. The odd electron spin(s) of the metal atom interacts with nuclei in the ligands via a dipolar interaction and shifts the nmr or endor signals. Analysis of these spectra allow one to obtain information on the relative position of nuclei in the ligand with respect to the central metal atom. These studies allow one to identify the structure of ligands near the metal atom and determine the local geometry of molecules surrounding the transition metal. Investigations will be conducted with model metal peptide complexes, metallonucleotides, metalloenzymes and metal complexes of nucleic acids. Pulsed nmr investigations to measure nuclear and electron spin relaxation times are also being conducted. Electron spin relaxation times depend on the relative position of the metal atoms in the complexes under investigation. These studies should allow one to determine the separation of metal atoms in metalloenzymes containing two or more metal atoms per molecules.